Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $238.38   13.133%   $269.6864   $269.69   $269.70   $269.70  
  Purchase #2 $209.94   7.140%   $224.9297   $224.93   $224.95   $224.90  
  Purchase #3 $214.99   12.582%   $242.04   $242.04   $242.05   $242.00  
  Purchase #4 $8.92   12.835%   $10.0649   $10.06   $10.05   $10.10  
  Purchase #5 $86.57   3.850%   $89.9029   $89.90   $89.90   $89.90  
  Purchase #6 $152.58   11.607%   $170.29   $170.29   $170.30   $170.30  
  Purchase #7 $15.57   7.167%   $16.6859   $16.69   $16.70   $16.70  
  7 purchase totals = $926.95       $1,023.5998   $1,023.60   $1,023.65   $1,023.60